@st-h I do no know more details about the Java drivers or how to find the cause of an aborted transaction.
It’s quite a surprise to find out this seems to not be possible at all with MongoDB.
Yes, I ran into a similar frustration. I had 3 tables to which I added validation. 2 worked; 1 did not. I searched and determined definitively there’s no way to cause MongoDB to log why a validation failed. There’s an open issue to add that feature.
Edit: I did figure out my problem after exhaustive trial-and-error … a misspelling in one place 
My takeaway is that, as good as MongoDB is, and I like it and use it daily, it’s not really “enterprise-ready”. It doesn’t have the completeness and stability of the mature relational products.